Junction of the Granite and the Killas Rods in Cornwall. 245 



of twenty feet; but further off, the constituent parts, the quartz 

 as well as the felspar, become larger and larger, and porphyritic 

 twin crystals of felspar begin to appear here and there ; so this 

 rock gradually passes into the character of the large-grained 

 granite, from which it is so evidently different at the junction of 

 both. As far as the steepness of the cliflPs allows access to the 

 mass of underlying granite, it does not yet assume the same ap- 

 pearance as the overlying large-grained granite ; but it cannot 

 be very doubtful that near the level of the sea a granite not dif- 

 ferent from that at the top of the cliffs would be found, if ac- 

 cess to it could be in any point obtained. The component 

 parts in both sorts of granite being quite the same, they only 

 differ one from the other by their texture' and different state 

 of crystallization. 



A vein of fine-grained granite occurs in the main body of 

 the large-grained granite near (n) fig. 27 ; it may be traced 

 for a considerable length in its direction ; it appears to start 

 from the main body of fine-grained granite, this being not 

 very far distant, and its mass bearing a near resemblance to 

 it. This vein is partly separated from the granite forming its 

 walls by an open interstice in which schorl frequently occurs. 

 Between the lines of section (e/) and (gh) occur several veins 

 of fine-grained granite coming out of the main body of granite 

 of the same nature ; — a vein of this kind is represented in the 

 section, fig. 24. 



Several granite veins occur on both walls of the cove (o) : 

 one, being a foot wide, represented fig. 28. is undoubtedly the 

 same which appears near the point (w); it runs 15 degrees 

 west of north, and is nearly perpendicular. Another vein un- 

 derlies rapidly, is ten inches wide, and heaved by two strings 

 of quartz. The granite in these veins is fine-grained, and ex- 

 actly of the same description as that of the main body of fine- 

 grained granite; the contents of the vein are very distinctly 

 separated from the large-grained granite forming the walls of 

 the veins. On the other wall of the cove (o), fig. 29. may be 

 traced chiefly the last-mentioned granite vein; this separa- 

 tion from the walls is so perfect, that large lioUows are found 

 on it by the action of the sea; the length for which the vein is 

 exposed to sight may be more than two hundred feet; at 

 last it joins another granite vein, which is thirteen feet wide 

 and nearly perpendicular. On both walls the granite in this 

 large vein is very fine-grained, but in the interior it becomes 

 of a larger size as to its constituent parts, and here it contains 

 more green mica and black schorl. Small strings go off from 

 this vein, which is intersected by open strings as well as the 

 granite forming its walls. The |)roniontory called Tol Pcdn 



IVnwith 



